Such a cooling-air cooler has been disclosed, for example, by European Patent Application EP-A1-0 773 349 of the applicant.
In gas-turbine plants it is normal practice to branch off some of the combustion air drawn in and compressed by the compressor as cooling air, to cool it down in a downstream cooling-air cooler and to use it for cooling thermally loaded parts of the turbine and/or the combustion chamber. If the gas-turbine plant, taken on its own, works in an open gas cycle (simple cycle), that is, for example, in a gas-turbine power plant, or in combination with a steam cycle (combined cycle), for example in a combined-cycle power plant in which the water/steam circuit is not installed until later (phased construction) or has failed for some reason or other, the cooling in the cooling-air cooler is effected by spraying in water and/or by external cooling.
If the gas-turbine plant works as part of a combined-cycle power plant, the heat extracted from the cooling air in the case of a cooling-air cooler of appropriate construction may be used to generate additional steam for the water/steam circuit.
In the publication mentioned at the beginning, a cooling-air cooler suitable for both applications is proposed, in which cooling-air cooler, in a pressure vessel, on the one hand, the cooling air to be cooled flows around spiral evaporator tubes in counterflow in the axial direction and, on the other hand, water can be sprayed into the cooling air on the inlet side of the cooling air (FIG. 3 of the publication). In addition, it is possible for some of the steam generated in the cooling-air cooler to be injected on the outlet side into the cooling air (FIG. 4 of the publication).
The direct spraying of water into the cooling air flowing through the cooling-air cooler is not without problems: if too much water is sprayed in, the cooling air will possibly contain water droplets when leaving the cooling-air cooler, and these water droplets may have a harmful effect during the cooling of the thermally highly loaded parts of the gas-turbine plant, for example due to erosion. If not enough water is sprayed in, the requisite cooling of the cooling air may possibly not be achieved. Since the thermal conditions with regard to the cooling air change during the transition between various operating states of the plant, the supply of water to the cooling-air cooler must be carefully controlled in order to avoid the abovementioned damage. This requires considerable control input.